This section is intended to provide a background or context to the invention recited in the claims. The description herein may include concepts that could be pursued, but are not necessarily ones that have been previously conceived or pursued. Therefore, unless otherwise indicated herein, what is described in this section is not prior art to the description and claims in this application and is not admitted to be prior art by inclusion in this section.
Dragline excavators typically have a bucket assembly that is controlled by wire ropes. Hoist ropes attach to the top of the bucket assembly and move the bucket vertically, while drag ropes attach to the back of the bucket assembly and move the bucket horizontally. Both drag ropes and hoist ropes are wrapped around a drum assembly, which pulls and releases the ropes as necessary to maneuver the bucket. As the ropes are pulled and released, one or more ropes may become slack (i.e. lose tension). The slack rope creates an unbalanced load for the drum assembly, often causing damage to the internal bearings of the drum assembly as the drums rotate. The slack rope may also cause the bucket to swing with limited control, damaging the bucket or other excavator components, or dumping the contents of the bucket. This slack rope condition may cause similar problems in rope shovels or other machinery utilizing wire ropes.
Typically, a single beam photometric transmitter/receiver module has been utilized to identify a slack rope condition within the drum assembly. The conventional module is positioned parallel to the drum rotation and configured to detect a slack rope condition prior to any major damage to surrounding components. However, conventional detection modules often do not detect the slack rope condition early enough to prevent damage. The conventional modules are often designed to rest in a position close to the top of the deck, rather than near the drum, which allows the modules to detect only the most severe slack rope conditions. Also, the conventional modules typically have only a single beam, and may not detect slack ropes that are out of the direct line of the single beam.
Conventional slack rope detection modules are also susceptible to false positives (i.e. the module indicates that a slack rope condition is present when the condition has not occurred). False positives result in inefficiencies necessitated by machine downtime to address the slack rope alert (e.g. operator alert, machine shutdown, etc.) produced by the detection module. Conventional detection modules are typically not adjustable, so that the module cannot be easily corrected in response to the false positives. Therefore, the detection module may continue to give false positives until the machine is removed from the field for service, resulting in additional machine downtime.
An example of another conventional slack rope detection module is found in U.S. patent application Ser. No. 13/231,114, filed Sep. 13, 2011, for “Cable Monitoring in Coiled Tubing.” This application discloses a cable slack monitoring feature configured to detect an accumulation of cable slack in a portion of coiled tubing. The detection module may include one or more monitoring features configured to collect data related to cable slack and tension. A control system may then analyze the data, comparing it with empirical data to identify whether a slack condition has occurred. One problem with this type of detection module is that it may not detect the slack rope condition early enough to prevent damage. Also, this conventional detection module is susceptible to false positives and may not be easily corrected in response to the false positives.